The research study was conducted to explore the relationship between the student teacher ratio and academic achievements at the secondary level in the subject of physics. The study was experimental research by nature so pre-test, post-test control group design was adopted and the sample of 127 students of 10th grade from Govt. High School Warburton out of the population of 287 students was divided into control and experimental groups with 40 students (control group) and 87 students (experimental group). Units (1-5) from the physics book 10th grade published by Punjab Text Book Board Punjab were selected as contents of study and two achievements tests (Pre & Post) in Physics were developed having 20 multiple choice items. The validity of the instruments was assured by the expert opinions of three experts and the reliability of the instruments was assured using testretest techniques having 0.837 Pearson’s product moment. Pre and post tests were administered to the Experimental and Control groups by the researcher along with the two other teachers and data was collected. The data collected were tabulated, mean score and standard deviation statistics were used to explore the answers of the research questions while the t- test statistics were employed to test the hypothesis for the analysis and interpretation of data. It was concluded from the analysis and interpretation of data that there exists an inverse relationship between academic achievements and student teacher ratio and was recommended that Government may ensure the implementation of the law of student teacher ratio at the secondary level